[R] creating lists of random matrices

[Uwe Ligges]

Not answering the question, but if you have the same dimensions of the 
matrices everywhere, it is much more efficient to sample all numbers in 
a row and put stuff into an array:

array(rnorm(5*4), dim=c(2,2,5)))

Best,
Uwe Ligges




On 09.11.2016 19:51, Marc Schwartz wrote:
>
>> On Nov 9, 2016, at 12:41 PM, Marc Schwartz <marc_schwartz at me.com> wrote:
>>
>>
>>> On Nov 9, 2016, at 12:32 PM, Evan Cooch <evan.cooch at gmail.com> wrote:
>>>
>>> So, its easy enough to create a random matrix, using something like (say)
>>>
>>> matrix(rnorm(4),2,2)
>>>
>>> which generates a (2x2) matrix with random N(0,1) in each cell.
>>>
>>> But, what I need to be able to do is create a 'list' of such random matrices, where the length of the list (i.e., the number of said random matrices I store in the list) is some variable I can pass to the function (or loop).
>>>
>>> I tried the obvious like
>>>
>>> hold <- list()
>>> for (i in 1:5) {
>>>   hold[[i]] <- matrix(rnorm(4),2,2)
>>>   }
>>>
>>>
>>> While this works, it seems inelegant, and I'm wondering if there is a better (more efficient) way to accomplish the same thing -- perhaps avoiding the loop.
>>>
>>> Thanks in advance...
>>
>>
>> Hi,
>>
>> See ?replicate
>>
>> Example:
>>
>> ## Create a list of 5 2x2 matrices
>
>
>
> Sorry, correction on my reply.
>
> I copied the wrong output, It should be:
>
>> replicate(5, matrix(rnorm(4), 2, 2), simplify = FALSE)
> [[1]]
>           [,1]      [,2]
> [1,] 0.9700486 1.4249251
> [2,] 0.7621312 0.8267747
>
> [[2]]
>           [,1]       [,2]
> [1,] 0.4517927  0.2047509
> [2,] 0.6336959 -0.6028124
>
> [[3]]
>           [,1]      [,2]
> [1,] 0.6468823 0.4268734
> [2,] 0.1664907 0.3905180
>
> [[4]]
>            [,1]       [,2]
> [1,] -0.3170839 -1.0113201
> [2,] -1.5356600  0.9658132
>
> [[5]]
>            [,1]       [,2]
> [1,] -1.1937503 -0.2653502
> [2,]  0.9319919  0.1780254
>
>
> The 'simplify' argument should be FALSE, so that an array is not created.
>
> Regards,
>
> Marc Schwartz
>
>
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>
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